In recent years, the performance of electronic component in an electronics field has been improved significantly and, thereby, increases in information processing speed, miniaturization of apparatuses, and expansion in functionality of information processing equipment, e.g., large computers, mobile communication terminals, and personal computers, have been facilitated.
A multi-chip module (MCM), in which a plurality of semiconductor devices, e.g., VLSI and ULSI, mounted on a ceramic substrate, is mentioned as one of such electronic components. In such modules, ceramic multilayer substrates including three-dimensionally disposed wiring conductors are used frequently in order to increase the mounting density of semiconductor devices and electrically favorably connect between individual semiconductor devices. The ceramic multilayer substrate is a laminate composed of a plurality of ceramic layers, and the surface and the inside thereof include wiring conductors for constituting circuits.
Regarding production of the ceramic multilayer substrate, it is known that there is a technical problem during firing in restriction of shrinkage of unfired ceramic layers in a plane direction. In order to solve this problem, two types of unfired ceramic layers having different sintering temperatures are laminated and fired so as to restrict shrinkage of the unfired ceramic layers in a plane direction, thereby taking advantage of a difference in shrinkage behavior. The above-described method may be referred to as a “shrinkage-compensation process” or the like.
FIG. 12 is a rough sectional view showing a known ceramic multilayer substrate produced by using the shrinkage-compensation process. As shown in FIG. 12, a ceramic multilayer substrate 70 has a structure in which first ceramic layers 71 formed from a first ceramic material and second ceramic layers 72 formed from a second ceramic material having a sintering temperature higher than the first ceramic material are laminated. Internal conductors 73 are disposed between the first ceramic layers 71 and the second ceramic layers 72, and external conductors 74 are disposed on the surfaces of the ceramic multilayer substrate 70. The internal conductors 73 and the external conductors 74 are electrically connected to each other by via conductors 75 penetrating the first ceramic layers 71 and the second ceramic layers 72 in a thickness direction.
Regarding production of the ceramic multilayer substrate 70, second ceramic green layers serving as the second ceramic layers 72 after firing functions in such a way as to restrict shrinkage of the first ceramic green layers serving as the first ceramic layers after the firing. (Refer to, for example, Patent Document 1.)
Patent Document 1: Japanese Unexamined Patent Application Publication No. 2000-315864